The present invention relates to an electric power supplying apparatus supplying electric power generated by an unstable electric power supply to a load and a control method therefor and, more particularly, to an electric power supplying apparatus supplying electric power generated by an unstable electric power supply, such as a solar cell, a wind power generator or a wave activated power generator, which generates variable electric power, as a power source to a load such as an electric motor, and a control method for controlling the electric power supplying apparatus.
Recently, global warming, exhaustion of fossil fuels, and radioactive contamination caused by accidents in nuclear power plants and radioactive wastes have become social issues, and the issues on the terrestrial environment and energy are rapidly attracting the interest of many people. In this situation, the solar cell, for example, which generates electric power from the solar ray that is an inexhaustible clean energy source, is anticipated as the energy source of tomorrow.
There are various sizes of systems using the solar cell, and the electric power required by those systems ranges from several watts to thousands of watts. Further, there are many types of systems: a system which directly uses electric power generated by the solar cell; a system which uses electric power generated by the solar cell to charge a storage battery; and a system which uses electric power generated by the solar cell along with commercial electric power, for example. Among these systems using the solar cell, a system suggested as a solar pump system for drawing water from source, such as a well and a river, for irrigation or drinking is very useful especially in some geographic regions, such as tropical regions, where the amount of insolation is large, and in unelectrified regions, because the running cost of the system and the load of transportation of fuels for running the system can be saved. Further, it is also advantageous for highly electrified cities to own a solar pump system as measures to cope with a natural disaster, such as an earthquake, since it is possible to supply water relatively easily by using the solar pump system in a case where the supply of electric power and water stops.
FIG. 2 is a diagram illustrating a configuration of a water supply system employing a solar pump system. In FIG. 2, direct current (DC) electric power obtained from a solar panel 1, i.e., an unstable electric power supply, is provided to a pump 3 via a pump driving unit 8. The water in a well 15 is drawn through a first liquid conveying pipe 11 up to a water tank 9. The water in the water tank 9 is supplied through a second liquid conveying pipe 16 and a valve 10.
However, the water supply apparatus as shown in FIG. 2 which uses the pump 8 run by electric power supplied only from the solar panel 1 shown in FIG. 11 may not be able to draw water up to the water tank 9 in the mornings and evenings, when an amount of insolation is small, and on cloudy days, since the electric power generated by the solar panel 1 becomes small, and thus although the pump 3 runs, the water does not reach a discharge opening 91.
In order not to waste the electric power generated by the solar cell when the amount of insolation is small, methods of using a plurality of low output pumps, as disclosed in Japanese Patent Application Laid-Open Nos. 56-132125 and 57-153531, as shown in FIG. 12, are suggested. However, the higher the output of a pump is, the better its efficiency. Therefore, by using a plurality of low output pumps to obtain a predetermined output and using a part of the pumps to supply water when the amount of insolation is small, less energy is wasted; however, the efficiency is still not good. Furthermore, the initial cost of the apparatus is high since a plurality of pumps are necessary.
Further, a method of driving the pump 3 while storing electric power generated by the solar panel 1 in a storage battery 5, as shown in FIG. 13, is proposed in Japanese Patent Application Laid-Open No. 60-74995. However, according to the configuration shown in FIG. 13, the operation voltage of the solar panel 1 is fixed to a voltage across the storage battery 5, therefore, the solar panel 1 is not operated at the maximum output point. Accordingly, the solar energy is not utilized efficiently.
The present invention has been made in consideration of the above situation, and has as its object to provide a reliable electric motor driving apparatus, having a simple configuration, which is run by electric power from an unstable power supply, such as a solar cell, capable of efficiently using electric power supplied from the unstable power supply, and a control method for controlling the electric motor driving apparatus.
According to the present invention, the foregoing object is obtained by providing an electric power supplying apparatus comprising, supplying means for supplying electric power generated by an unstable electric power supply to a load, electric power storage means which is connected to the unstable electric power supply in parallel, switching means which is connected between the unstable electric power supply and the electric power storage means in series, and control means for controlling the opening and closing of the switching means and controlling an operation of the supplying means in dependence upon an output from the unstable electric power supply.
The foregoing object is also attained by providing a control method for controlling an electric power supplying apparatus having, supplying means for supplying electric power generated by an unstable electric power supply to a load, electric power storage means which is connected to the unstable electric power supply in parallel, and switching means which is connected between the unstable electric power supply and the electric power storage means in series, the method comprising the steps of opening the switching means during a predetermined period, closing the switching means outside of the predetermined period, and controlling an operation of the supplying means depending upon an output from the unstable electric power supply.
Furthermore, the foregoing object is also attained by providing a control method for controlling an electric power supplying apparatus having, supplying means for supplying electric power generated by an unstable electric power supply, electric power storage means which is connected to the unstable electric power supply in parallel, and switching means which is connected between the unstable electric power supply and the electric power storage means in series, the method comprising the steps of opening the switching means when output electric power of the unstable electric power supply exceeds a predetermined value, closing the switching means when the output electric power is equal to or less than the predetermined value, and controlling an operation of the supplying means depending upon an output voltage of the unstable electric power supply.